por ke yo uso este codigo y nomas no puedo poner la imagen de fondo Código Delphi
[-]email := TIdMessage.Create(nil);
email.From.Text := 'mi correo';
email.Recipients.EMailAddresses := 'a donde va';
email.Subject := 'Hello';
email.ContentType := 'multipart/mixed';
email.IsEncoded:=true;
email.Body.Assign(html);
txtpart := TIdText.Create(email.MessageParts);
txtpart.ContentType := 'text/plain';
txtpart.Body.Text := '';
htmpart := TIdText.Create(email.MessageParts, html);
htmpart.ContentType := 'text/html';
bmppart := TIdAttachment.Create(email.MessageParts, filename);
bmppart.ContentType := 'image/jpeg';
bmppart.FileIsTempFile := true;
bmppart.ContentDisposition := 'image';
bmppart.ExtraHeaders.Values['content-id'] := '\homerorx.jpg';
bmppart.DisplayName := '\homerorx.jpg';